Effect Of Interphase Research Articles

Investigation of interphase effects in silica-polystyrene nanocomposites based on a hybrid molecular-dynamics-finite-element simulation framework.

A recently developed hybrid method is employed to study the mechanical behavior of silica-polystyrene nanocomposites (NCs) under uniaxial elongation. The hybrid method couples a particle domain to a continuum domain. The region of physical interest, i.e., the interphase around a nanoparticle (NP), is treated at molecular resolution, while the surrounding elastic continuum is handled with a finite-element approach. In the present paper we analyze the polymer behavior in the neighborhood of one or two nanoparticle(s) at molecular resolution. The coarse-grained hybrid method allows us to simulate a large polymer matrix region surrounding the nanoparticles. We consider NCs with dilute concentration of NPs embedded in an atactic polystyrene matrix formed by 300 chains with 200 monomer beads. The overall orientation of polymer segments relative to the deformation direction is determined in the neighborhood of the nanoparticle to investigate the polymer response to this perturbation. Calculations of strainlike quantities give insight into the deformation behavior of a system with two NPs and show that the applied strain and the nanoparticle distance have significant influence on the deformation behavior. Finally, we investigate to what extent a continuum-based description may account for the specific effects occurring in the interphase between the polymer matrix and the NPs.

Effect of interphase properties on fracture behavior of TCP/PLA composites

In the present study, the effects of interphase on the mechanical properties of β-tricalcium phosphate (β-TCP) particle-dispersed bioabsorbable poly(lactic acid) (PLA) composites were investigated. In order to improve interfacial strength between PLA and β-TCP, the surface of β-TCP was modified with L-lactic acid (LLA) monomer. The weight ratios of LLA to β-TCP are selected as 1.5, 3, 4.5, 6, 7.5%. Tensile strength decreased with the incorporation of β-TCP to PLA, whereas the tensile strength of composites was improved in the case of modification with the weight ratio of 3%. From acoustic emission measurements, initial interfacial debonding was also suppressed up to 3%. From finite elemental analysis, elastic modulus of interphase is about 30–70% of that of PLA and elastic modulus of the composites do not depend on interphase thickness. From the stress distributions at initial debonding onset, it is clarified that interfacial debonding is caused by shear stress between particle and interphase and interfacial shear strength seems to be about 20 MPa.

Effect of PyC interphase thickness on mechanical and ablation properties of 3D Cf/ZrC–SiC composite

Three-dimensional (3D) Cf/ZrC–SiC composites were successfully prepared by the polymer infiltration and pyrolysis (PIP) process using polycarbosilane (PCS) and a novel ZrC precursor. The effects of PyC interphase of different thicknesses on the mechanical and ablation properties were evaluated. The results indicate that the Cf/ZrC–SiC composites without and with a thin PyC interlayer of 0.15µm possess much poor flexural strength and fracture toughness. The flexural strength grows with the increase of PyC layer thickness from 0.3 to 1.2µm. However, the strength starts to decrease with the further increase of the PyC coating thickness to 2.2µm. The highest flexural strength of 272.3±29.0MPa and fracture toughness of 10.4±0.7MPam1/2 were achieved for the composites with a 1.2µm thick PyC coating. Moreover, the use of thicker PyC layer deteriorates the ablation properties of the Cf/ZrC–SiC composites slightly and the ZrO2 scale acts as an anti-ablation component during the testing.

Boron Modified Phenol Formaldehyde Derived Cf/SiBOC Composites with Improved Mechanical Strength for High Temperature Applications

Ceramic matrix composites (CMCs) are potential thermo-structural materials for use in space applications. Fiber/matrix (F/M) interface plays a key role in determining the mechanical properties of CMCs. Present study focuses on the optimization of F/M volume ratio and the influence of Pyrocarbon (PyC) interphase coating on the mechanical properties of CMCs derived from precursor route. CMCs are fabricated using phenol formaldehyde (PF) resin and boron modified PF (BPF) resin as precursor slurries, 2D carbon fabric (Toray, T300 3K, 8H, satin weave) as reinforcement and PyC as interphase. The deposition of PyC interphase was done by chemical vapor infiltration on the carbon fabric followed by densification of the matrix using reaction bonded silicon carbide method. In CMCs prepared from PF resin, without interphase the flexural strength improves from 25 ± 3.9 MPa (fiber content-40) to 63 ± 9.9 MPa (fiber content-60) on increasing the fiber vol%. In the second part of the investigation, the effect of PyC interphase was studied using CMCs prepared from BPF resin with fiber volume ratio of 60 %. The CMCs with PyC interphase shows an improvement in flexural strength (102 ± 11.5 MPa) compared to that of CMCs prepared without interphase (38 ± 4.4 MPa). The fractography of CMCs with and without interphase was closely evaluated under a scanning electron microscope. CMCs without interphase show no fiber pull-out, indicating the strong fiber-matrix bonding. While CMCs with interphase show fiber pull-out phenomenon and hence fails in a ductile manner.

Kinetics of Hg° oxidation over a V2O5/MoO3/TiO2 catalyst: Experimental and modelling study under DeNOX inactive conditions

In this work, a kinetic study of mercury oxidation over a commercial plate-type V/Mo/Ti/O catalyst was addressed by investigating the effects of key operating variables (temperature, HCl and Hg° concentration). The study was performed under reference DeNOX-inactive conditions, that is in the absence of NOX, NH3, SOX, recognizing that surface coverage effects can greatly affect the kinetics of this complex reacting system. Aim of the work was in fact to better clarify the nature of the intrinsic reaction (in particular its temperature dependence), that, despite the increasing interest toward this reaction, is still debated with a very large scatter among observations. The experiments were performed over slabs. The combined effects of temperature and HCl concentration evidenced that the conversion of Hg° was independent from the HCl content below 300–325°C, where the reaction showed a positive temperature dependence; at higher temperature, the conversion of Hg° became highly sensitive to the HCl concentration, which determined the observed temperature dependence (negative at 2.5ppm HCl, positive at 50ppm HCl). Thus the data suggest a strong dependence of the reaction kinetics on the surface coverage of HCl.A model of the reactor cell was developed and an engineering analysis of data was performed to decouple the effects of inter-phase and intra-porous mass transfer limitations. A rate expression was derived from the formalization of a redox reaction scheme wherein a step-wise oxy-chlorination process (Hg°→HgClads→HgCl2) is assumed in line with recent theoretical findings. By assuming that the surface coverages of the HgCl intermediate and the reduced sites are negligible with respect to the coverage of free and chlorinated oxidized sites, a simple rate expression is derived which accounts for a quadratic dependence on HCl coverage and a linear dependence on the gas-phase concentration of elemental mercury (in line with the experimental evidence). The whole bulk of data could be well described, capturing the key observed trends. The activation energy of the reaction steps was found to be 14000cal/mole while the enthalpy of HCl activation was estimated at −20000cal/mole, coherently with the energetics of V-sites chlorination.

Interphase Models for Nanoparticle-Polymer Composites

AbstractIn this work, the interphase effects of nanoparticle enhanced polymer composite materials are investigated. Three interphase models based on finite size representative volume element (RVE) are proposed to estimate the effective material properties of nanoparticle-polymer composites, including” (1) The finite Eshelby tensor based shell model, (2) An improved double inclusion model, and (3) A modified Hashin-Shtrikman model. These micromechanics models are employed to analyze the interphase phase effects on the effective material properties of nanoparticle-polymer composites. One crucial factor that influences the strength of nanoparticle enhanced polymer composites is the material properties of the interphase between nanoparticles and the corresponding polymer matrix. These three improved micromechanics models are designed to incorporate interphase effects. Using the interphase models, the authors estimate the effective Young’s and shear moduli for a set of four material systems of silica nanoparti...

Influences of Closing Phase Angle and Frequency on Electrodynamic Stability of Air Circuit Breaker

Short-time withstand current ( $I_{\mathrm{ cw}}$ ) is an important parameter for air circuit breakers (ACBs) and easily causes electrodynamic stability problems. This paper is aimed to investigate the influences of the closing phase angle and frequency on the electrodynamic stability of ACB. Considering the skin effect, the interphase effect, and the nonlinear B–H characteristics of ferromagnet, a calculation model of a three-phase ACB is built based on the 3-D transient finite-element method. It is found that the movable conductors A5, B1, and C1 show the worst electrodynamic stability when the closing phase angle ( $\psi $ ) is equal to $\varphi -\pi $ /2, $\varphi +\pi $ /6, and $\varphi +5\pi $ /6, respectively, where $\varphi $ is the phase angle difference between the voltage and the current. With the frequency increasing from 50 Hz to 100 and 200 Hz, the slope-shaped distribution of peak currents and repulsion forces in phases B and C is changed to the valley-shaped distribution, and the peak current of B1 is increased by 20% and 38.6% at the beginning stage of $I_{\mathrm{ cw}}$ , and by 12.5% and 26.4% at the periodic stage of $I_{\mathrm{ cw}}$ , respectively. In addition, the peak lateral forces of the movable conductors adjacent to other phase are also increased considerably by increasing frequency.

Micromechanics-based viscoelastic analysis of carbon nanotube-reinforced composites subjected to uniaxial and biaxial loading

Viscoelastic response of carbon nanotubes (CNTs) reinforced polyimide nanocomposites subjected to the action of uniaxial and biaxial loads is studied using a micromechanical model based on the unit-cell method. The developed micromechanical model is simple and efficient, and provides closed-form expressions for the effective viscoelastic response of nanocomposites. The representative volume element (RVE) of nanocomposites consists of three phases including continuous CNTs, polyimide matrix and interphase. The state of dispersion of CNTs into the polymer matrix is considered to be random. The obtained elastic and viscoelastic responses are found to be in good agreement with those predicted through other methods and experimental data. The model is then used to study the effects of interphase materials (elastic and viscoelastic) on the creep behavior of nanocomposites. Also, the effects of stress level, CNT radius and interphase on the viscoelastic response of nanocomposites under uniaxial and equi-biaxial including transverse/transverse and longitudinal/transverse loading conditions are examined.

Impact of the Native SiO2 Surface Layer on the Electron Transfer at Amorphous Si Electrodes

The electron transfer at uncharged microstructured and planar amorphous (a-)Si was characterized using the feedback mode of scanning electrochemical microscopy (SECM) and 2,5-di-tert-butyl-1,4-dimethoxybenzene as redox mediator in carbonate electrolytes. Approach curves and images demonstrate that the electron transfer rate at pristine a-Si is relatively small due to the native SiO2 surface layer. In addition, the electron transfer rates show local variations because of the heterogeneous coverage of SiO2. After removal of the SiO2 layer, the effect of the solid electrolyte interphase (SEI) on electron transport rate can be studied. The SiO2 layer is at least partially removed by approach curve contact and scratching with the microelectrode probe. After SiO2 removal, the electron transfer rates increase strongly and remain heterogeneous.

Bridging tensor with an imperfect interface

Abstract Bridging tensor is fundamental to the Bridging Model for prediction of thermomechanical and strength behaviors of a fiber reinforced composite based on constituent fiber and matrix properties. This paper focuses on derivation of the bridging tensors with an imperfect fiber–matrix interface. Using a three-phase coaxial cylinder assemblage (CCA) model, the stress fields in all of the three materials in the assemblage when subjected to six kinds of loading conditions are obtained by means of rigorous elasticity theory. The stresses are then averaged with respect to the corresponding phase volumes. By imposing that the averaged stress components in each phase be correlated with those in an adjacent phase through a bridging tensor and solving the resulting simultaneous linear algebraic equations, the bridging tensor elements are determined. Comparison of the thus obtained effective off-axis moduli with experiments for a SCS-6/Ti unidirectional (UD) composite is made to show the efficiency of the three-phase bridging tensors. Effect of interphases on the effective elastic properties and stress ratios of the composite with different coatings is investigated.

3-D Transient Finite-Element Analysis and Experimental Investigation of Short-Circuit Dynamic Stability for Air Circuit Breaker

Short-time withstand current ( $I_{\mathrm{ cw}}$ ) is a crucial parameter of air circuit breakers (ACBs) due to the selective protection. Considering the skin effect, the interphase effect, and the nonlinear $ {B}$ – $ {H}$ characteristics of ferromagnet, the 3-D transient finite-element method is adopted to analyze the short-circuit dynamic stability of a three-phase ACB. The transient current, the repulsion torque, the tilting torque, and the sliding torque on each movable conductor are calculated at the beginning stage and the periodic stage of $I_{\mathrm{ cw}}$ , respectively. It is found that the electromagnetic torque tilts and slides the outer movable conductors toward the middle of each phase. The movable conductors of phase B perform the worst in the aspect of dynamic stability. The relevant experiments are also conducted to investigate the dynamic stability through observing the position, the size, and the sliding trace of the erosion marks on contact tips. Based on the proposed calculation model, it is found that installing ferromagnet plates on both the sides of movable conductor groups can enhance the dynamic stability.

Effect of nanofiller shape on viscoelasticity of rubber nanocomposite investigated by FEA

Abstract Based on the micromechanical theory, the effect of the shapes of nanofillers on the viscoelasticity of rubber nanocomposites was evaluated by the finite element analysis. The shapes of nanofillers we discussed included sphere, cylinder, tube, plate, ring, and spring. Two types of interphase – “bonding interphase” and “frictional interphase” – which represented the strong interphase and the weak interphase respectively were assumed to discuss the effect of interphase on the viscoelasticity of rubber nanocomposites. The dissipation and loss factors were calculated and discussed. The predicted results show that the shapes of nanofillers have great effect on the viscoelasticity of rubber nanocomposite. Including the spring nanofillers in the rubber matrix can greatly decrease the loss factor of the nanocomposite when the interphase is a “bonding interphase,” while including the ring nanofillers in the rubber matrix can greatly increase the loss factor of the nanocomposite when the interphase is a “frictional interphase.”

Statistical multiscale homogenization approach for analyzing polymer nanocomposites that include model inherent uncertainties of molecular dynamics simulations

A statistical multiscale homogenization strategy of polymer nanocomposites is proposed to account for the inherent uncertainties of molecular dynamics (MD) simulations. The proposed statistical multiscale homogenization scheme includes a discrete MD simulation system, a continuum theory of micromechanics of Eshelby's solution and two-scale homogenization, and Monte-Carlo simulations. The means and standard deviations of the elastic properties of the nanocomposites are quantified and discussed through statistical analyses that show the interphase effect. The elastic properties of the matrix, interphase, and composites are assumed to follow a lognormal distribution. An iterative inverse algorithm for obtaining the probability density distribution of the interphase is proposed and validated.

Effects of CVD SiBCN interphases on mechanical and dielectric properties of SiCf/SiC composites fabricated via a PIP process

SiBCN coatings were successfully prepared on KD-II SiC fibers via a chemical vapor deposition (CVD) process utilizing borazine and liquid polycarbosilane as precursors. Fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS) indicated the coating contained B–N, Si–C, C–C and Si–N bonds. Effects of the CVD SiBCN interphases on mechanical and dielectric properties of SiCf/SiC composites fabricated via a PIP process were investigated. The results showed that the composites with CVD SiBCN interphases exhibited an obvious toughened fracture behavior, and the flexural strength was about 2.25 times than that of the composites without SiBCN interphases. The composites containing SiBCN interphases had a higher strength retention ratio than that containing BN interphases. Furthermore, SiBCN interphases improved the fracture strength evidently, but hardly had influence on the dielectric properties of the SiCf/SiC composites.

Stochastic analysis of the interphase effects on the mechanical properties of clay/epoxy nanocomposites

The polymeric clay nanocomposites are a new class of materials which recently have become the center of attention because of their superior mechanical and physical properties. Several studies have been performed on the mechanical characterization of these nanocomposites; however most of those studies have neglected the effect of the interphase and interfacial region between the clays and the matrix despite of its significance on the mechanical performance of the nanocomposites. Based on a hierarchical multiscale approach on the mesoscopic level, in this study we use the stochastic analysis and the computational homogenization method to analyse the effect of thickness and stiffness of the interphase region on the overall elastic properties of the clay/epoxy nanocomposites. The results show that considering interphase layer reduces the stiffness of clay/epoxy nanocomposites and this decrease becomes significant in higher clay contents. Then, the significance of the stiffness and thickness of the interphase layer on the elastic modulus of clay/epoxy nanocomposites are studied using a sensitivity analysis. Finally, the results of this study are validated with available experimental results.

The strengthening effect of carbon nanotube in metal matrix composites considering interphase

The formation of interphase around carbon nanotube (CNT) has been observed experimentally in metal matrix composites (MMCs). However, the characterization of mechanical behavior of interphase and its contribution to the elastoplastic response of MMCs are still open issues. In this paper, a theoretical model is developed to describe the coupled impact of interphase and load transfer effect induced by the reinforcement on the overall mechanical behavior of CNT-reinforced MMCs. The plastic property of interphase is addressed by the rate-dependent amorphous plasticity model. The effective elastic modulus of MMCs is considered to be sensitive to the content of interphase, and the introduction of interphase can obviously enhance the overall strength of the composites. In addition, the effects of matrix grain size, the content and size of the reinforcement have also been addressed in details. The comparisons between the predictions and available experimental data have been performed to validate the applicability of the proposed scheme.

A new special coating/fiber element for analyzing effect of interface on thermal conductivity of composites

The effects of interface or interphase on micro- and macro-thermal behaviors of square-pattern unidirectional fiber-reinforced composites are investigated. The interfacial phase is modeled by a thin layer coated on the surface of the fiber to resist radial and circumferential thermal expansion of the fiber. Making use of the periodicity of the composite, a basic unit cell containing one fiber is used to analyze numerically the states of temperature by way of a novel special coating/fiber element model developed in this paper. The element is established by employing special fundamental solutions which exactly satisfy the governing equations of heat transfer and the interfacial continuity between the filler and the interfacial phase in the unit cell. Subsequently, the mesh reduction effect, convergence, and accuracy of the present special coating/fiber element are verified by comparison with those from conventional finite element methods. Then, the effective thermal conductivity of several composites is analyzed for various values of the interfacial parameters including thickness and thermal properties under different fiber volume fractions to numerically reveal the role of the interface.

Role of the solid electrolyte interphase on a Li metal anode in a dimethylsulfoxide-based electrolyte for a lithium–oxygen battery

The effect of the solid electrolyte interphase (SEI) on a Li anode on the charge–discharge cycling performance in 1 M LiTFSI/dimethylsulfoxide electrolyte solution is examined by using charge–discharge cycling. The chemical structure of the surface and interior of the SEI strongly affects the cycling performance of the anode. The observed coulombic efficiency is low (<45%) when organic compounds such as lithium alkyl carbonates and polycarbonate form predominantly on the surface and interior. However, when inorganic compounds such as Li2CO3, Li2O, and LiF form instead, the coulombic efficiency increases to >85%. This enhanced efficiency remains constant regardless of the O2 content and despite <1000 ppm concentration of the contaminant H2O in the electrolyte. Thus, the lithium surface should be protected by inorganic compounds prior to cycling to prevent it from undergoing side reactions with the electrolyte during cycling in the electrolyte.

Effect of BN Interphase Coating and PIP Cycles on the Mechanical Properties of VSI SiC/SiC Composites

2.5D SiC/SiC composites with and without BN interphase coating were fabricated by VSI process from SiC/C preforms that were produced after 3, 4 and 5 PIP C cycles, respectively. The effect of the BN interphase coating and PIP C cycles on the mechanical properties and microstructure of the composites was investigated. The results indicated that the composites with or without BN interphase coating exhibited catastrophic fracture behavior. Both the excess residual carbon and BN interphase coating played a positive role in protecting the SiC fibers from silication by vapor silicon, which accounted for the less obvious fibers pull-out phenomenon that occurred in the composites. The PIP cycles had an influence on the residual porosity and the content of the newly developed SiC in the composites, and therefore the mechanical properties of the composites were influenced. The composites fabricated from preforms after 4 PIP C cycles and containing BN interphase coating have a flexural strength of 122.5 MPa and a modulus of 86.5 GPa.

Interphase effect on the macroscopic elastic properties of non-bonded single-walled carbon nanotube composites

Compared to the small diameter of a carbon nanotube (CNT), the thickness of the CNT–matrix interphase in a CNT–composite is considerable. Hence, the interphase property can significantly influence the macroscopic properties of the composite. This paper applies an effective multi-scale method to explore such an interphase effect on the properties of nano-composites reinforced by single-walled CNTs. The method integrates the van der Waals (vdW) gap interphase, the dense interphase, and the randomly distributed wavy CNTs in a matrix to realize an accurate prediction of macroscopic properties with a nanoscopic resolution, by using a conventional finite element code commercially available. The study concluded that with the same volume fraction, increasing CNT waviness and diameter reduces the composite Young's modulus, and that ignoring either the vdW gap interphase or the dense interphase can lead to an erroneous characterization, and that both interphases can be ignored in some circumstances.